typedef matchall-string-type {
type string {
pattern "\*";
}
description
"The string containing a single asterisk '*' is used
to conceptually represent all possible values
for the particular leaf using this data type.";
}

It should say:

typedef matchall-string-type {
type string {
pattern '\*';
}
description
"The string containing a single asterisk '*' is used
to conceptually represent all possible values
for the particular leaf using this data type.";
}

Notes:

As per RFC6020, Section 6.1.3., a backslash within a double-quoted string introduces a special character. The only valid escape sequences inside a double-quoted YANG string are: \n, \t, \" and \\. As \* is not a valid escape sequence, a single quoted string should be used to specify the offending pattern statement's argument. The quotes could also be omitted.